Such a method has become known from the DE-A-37 07 745. Since the respective preceding roller mill has to process coarser particles, it is to be understood that a control in the coarse range can thus be carried out relatively well. On the other hand, it will also be understood that due to the path from the preceding roller mill to the postponed one, the recovery time constant is relatively great. In practice there will therefore result a sort of proportional-integral-characteristic. This relatively long recovery time constant possibly causes deviations from the nominal value of the particle size to remain unstabilized for a relatively long time.
Now, the DE-C-31 53 304 shows a way how the grinding gap of a multi-roll mill, as the postponed roller mill will generally be, can be controlled over the axial length of the rollers in a relatively troublefree manner, e.g. according to a proportional-differential-characteristic, with respect to the control behavior and the uniformity of the gap adjustment or the layer thickness resulting therefrom. This control takes place by adjusting the number of rotations of the feed-in roller shaft in dependence upon the layer thickness measured. However, it has to be taken into account that also the feed-in rollers accomplish a grinding power. Therefore, when changing the introduction of energy into the mass, the flow characteristics will also be changed, particularly the flow limits, which, in the case of chocolate, may ultimately also affect the conching time. In the literature of the prior art, the phenomenon has been mentioned that chocolate masses which apparently have been processed in a completely uniform way and have the same composition of substances, may yield differing qualities after the conching. For this reason, regular flow characteristics of the material, particularly of cocoa mass or chocolate, brought about by controlling the roller speed on the basis of the differing specific energies introduced into the mass, will lead to different results, which is undesirable with a view to holding constant the quality. The entire contents of this DE-C- shall be incorporated herein by reference.